Quantifying muscle firmness is important in many areas of physiological research and clinical diagnosis. Specifically, quantifying muscle firmness can aid understanding of muscle operation; show the effect of physical fitness theories that have been applied to muscle groups; and enable doctors and researchers to better understand the causes of bone loss. The determining of tissue firmness is also important in the detection of heterogeneity in flesh and organs. Much research and development has gone into creating a sensor that can find breast and colon tumors by finding local differences in tissue firmness.
Many methods and instruments have been devised in the measurement of firmness. Ultrasonic and magnetic resonance imaging are popular methods but have the disadvantages of being expensive and bulky. With the objective of being able to determine firmness by “feel”, the indentation or palpation of an object in conjunction with a force measurements to determine tissue firmness has been well addressed in the prior art as described below.
A muscle tonometer device is described in Roush U.S. Pat. No. 5,038,795 and reproduced as FIG. 26. It measures the firmness of a muscle by measuring the force/displacement of a tissue sample captured by a pair of calipers 416. This technique limits its scope to tissues which can be sandwiched between parts of the measurement apparatus which the present invention seeks to avoid. In particular, it is not possible to use such a device to map the structure of the user's lower back with access only to the user's dorsal side.
In two of Sarvazyan's patents; U.S. Pat. Nos. 5,524,636 and 5,833,633, and in Sarvazyan's U.S. Pat. Application No. 20020004630, a roller 406 is shown opposite a force sensing array 408 with breast tissue 410 between the roller 406 and the force sensing array 408 (FIG. 27). The roller 406 deforms the tissue sample 410 and the sensing array 408 will detect if the roller 406 passes a mass of differing elasticity in the tissue by the spatial shifting of the mass inside the tissue being examined. While Sarvazyan's invention uses a roller 406 to apply an excitation force, it has the same limitation as Roush's prior art-namely, that this technique limits its scope to tissues that can be sandwiched between parts of the measurement apparatus which the present invention seeks to avoid.
Leveque U.S. Pat. No. 4,159,640 (FIG. 29) measures the firmness of a tissue sample 410 with a single indenter 412 surrounded by an annular footed base 414 which surrounds the indenter 412. Once a prescribed foot pressure is achieved, the device captures the displacement of the indenter 412 relative to the footed base 414. This technique is useful in getting crude firmness measurements from one side of a sample but lacks the ability to capture a continuous force/indentation curve and the ability to roll across a surface. Furthermore, the described annular configuration would be difficult to adapt to rolling contact.
In Laird U.S. Pat. No. 5,833,634, one embodiment of a tissue examination device is a roller ball indenter which is used for palpating breast tissue in a search for tumors, FIG. 28. The roller ball 400 gives the benefit of facilitating movement of the probe over the tissue sample 410. This roller ball 400 is mounted with three force-instrumented biasing springs 402 in contact via cylindrical rollers 404 with the back surface of the roller ball 400. The force data measured by the biasing springs 402 is used to calculate the force vector of the reaction of the roller ball 400 being pressed and rolled over the tissue sample 410. Since these sprung force sensors 402 are behind a rigid roller ball 400, the forces experienced by the sensors 402 are undesirably coupled. The device so described can detect boundaries of areas at different heights or firmnesses but cannot measure the firmness of a homogeneous local area when the probe is wholly over that area-it can only detect boundaries between areas of different firmnesses.
Lasky U.S. Pat. No. 6,190,334 describes the imaging of breast tissue firmness with a sensor-equipped probe as shown in FIG. 30. In one embodiment the probe tip is fitted with a roller 420. This method requires that the tissue sample 410 be fixtured between the roller probe 420 and the table 418 which prevents the tissue sample 410 from moving away from the roller probe 420. This has the same limitation as Roush's prior art. In another embodiment, the sensor consists of a tactile array.
Ladeji-Osias, in her Ph.D. thesis, “The Biomechanics of Breast Palpation: Single and multi-probe indentation tests”, describes a multi-prong soft tissue indenter as illustrated in FIG. 31. The three ball tips 430 contact the tissue sample while three linear differential transformer (LVDT) displacement sensors 422 measure the displacement of each of the prongs. Guide rods 428 maintain linear alignment of the outer prongs which are cantilevered to reduce the distance between the ball tips 430. A connecting frame 424 connects the three LVDT bodies 422 to a force load cell 426 which is itself mounted to a reference plane. The apparatus is designed to approximate the use of three fingers to manually palpate a breast (pg. ii). This thesis does not distinguish the advantage of a multi-prong indenter over a single-prong indenter aside from the multi-prong indenter mimicking the use of multiple fingers to manually palpate the breast tissue. They note, “To the best of our knowledge, no information on multi-probe indenters of this nature is available in the literature” (pg. 88). They note that surface friction affects measurements of friction and they experiment with use of water or Vaseline lubrication (pps. 107, 127, 136, and 139) but do not consider the use of rolling contact with the tissue sample. They note “The middle force consistently causes a larger displacement than the side forces” (pg. 70) but they fail to note that the displacement differential between the middle and the side probes is affected by the firmness of the sample.
Quantifying muscle firmness is important in automated massage. Specifically, quantifying firmness of localized regions of the back can allow a controller to adapt a massage pattern to avoid superficial bones such as the scapulae whose location varies between users. This information can also be used to concentrate on (or avoid) massaging areas with excessive muscle firmness (knots and spasms).
In Ookawa, U.S. Pat. No. 5,792,080 an automated massaging apparatus having self-adjusting massage pressure is disclosed. This invention maintains a desired massaging pressure by extending the roller towards the user until a reactive force is achieved. This mechanism accommodates the varying curvature of different users' backs whereby some users' lumbar back areas are more concave than others. However, Ookawa's invention does not measure firmness of a local area of the user's back and therefore cannot, for example, automatically accommodate itself to users with scapulae in different locations or detect muscle knots and concentrate massage on these areas.
Force/indentation measurements are also used in the rating of foams and the grading of fruit. However, the aforementioned patents and papers describe the most related prior art of which the applicant is aware. Accordingly, there is a need in the art for an improved method and apparatus for measuring firmness.